Instead of a normal character, during your organization phase you may bring into play one character (including a minion agent) with up to a 6 mind. Place this card with the character. -1 to his mind to a minimum of 1. Such a character may also be in your starting company.

Nothing disables the ability of Thrall of the Voice once it is placed on a character. That means that during your organization phase, you may always opt to bring in one character instead of a normal character, moving Thrall to the new character played.

Remember, NetRep rulings are official. This does not necessarily mean they are correct.

You probably aren't playing Fallen Wizards correctly. This prompted the backlash erratum that I will link to as soon as I notice it is officially posted.

In my first organization phase, I use the ability to play one character, replacing the opportunity to play a normal character.

Next organization phase, I have an opportunity to play a normal character. According to the text of Thrall of the Voice, I can instead play one character (including an agent) with up to 6 mind. Thrall is then placed on the character just played.

Remember, NetRep rulings are official. This does not necessarily mean they are correct.

You probably aren't playing Fallen Wizards correctly. This prompted the backlash erratum that I will link to as soon as I notice it is officially posted.

"Instead of a one normal character, during your organization phase you may bring into play one character (including a minion agent) with up to a 6 mind. Place this card with the character. -1 to his mind to a minimum of 1. Such a character may also be in your starting company."

I think the important part would be to disable the ability once it's on a character, so:

"If this card is not placed with a character, during your organization phase, instead of a normal character, you may etc."

Highlighting the differences underlined, I note that this card currently is not placed "on" a character, it is placed "with" a character... perhaps this would argue that it shouldn't be discarded if the character is removed from play? Certainly not the way I've played it up to now; what about the rest of you?

In a thematic sense, though, if the card is meant to represent the thralling voice of the wizard I don't see why it should leave play when the character leaves play. "For some the spell lasted only while the voice spoke to them, and when it spoke to another they smiled, as men do who see through a juggler's trick while others gape at it." If the enthralled character dies/runs off, why shouldn't the voice speak to another? But perhaps then if one opts to use it to bring another character into play, any previously enthralled character should be discarded if not already removed from play.

It is not our part here to take thought only for a season, or for a few lives of Men, or for a passing age of the world.

The only reference I've found that might pertain to the OP is below. Underline mine:

CoE66 wrote:In Digest #65, I ruled:
*** You cannot play Thrall of the Voice outside of your organization phase, but a Thrall in play that is not on another character can be used after a successful influence attempt after which you play the character in question.

Miika Karmitsa rightly pointed out:
Looks like that isn't possible: (emphasis mine)
Thrall of the Voice
Instead of a normal character, DURING YOUR ORGANIZATION PHASE you may bring into play one character (including a minion agent) with up to a 6 mind. Place this card with the character. -1 to his mind to a minimum of 1. Such a character may also be IN YOUR STARTING COMPANY.
*** Amend my ruling above from Digest #65 to remove the statement claiming that you can use Thrall of the Voice with an influence attempt.

Influence attempt aside, this could be read (via absence otherwise) as implying that the Thrall of the Voice can only be used when not on a character. Of course, as this netrep was so fond of saying, "if it isn't there, it isn't there". So in the current rules set I'd say Thrall of the Voice could be used even if currently with a character.

I like Konrad's direction of thought, although more clarity does seem helpful to avoid afresh allowance each organization phase:
"Instead of a normal character, during one of your organization phases you may bring into play one character (including a minion agent) with up to a 6 mind."

It is not our part here to take thought only for a season, or for a few lives of Men, or for a passing age of the world.